1. Field of the Invention
The present invention is generally related to a position sensor and, more particularly, to a system by which the position of a shift assist mechanism can be accurately determined.
2. Description of the Related Art
Those skilled in the art of marine propulsion systems are aware of many different types of gear shift mechanisms. In addition, the skilled artisan is familiar with shift assist devices.
U.S. Pat. No. 3,580,278, which issued to Bennett on May 25, 1971, describes a fluid actuated transmission control. A pneumatic or hydraulic control mechanism for power shift transmissions of the type used in heavy duty power equipment, such as earth moving machines, cranes and material handling devices, marine equipment, deep well drilling rigs, and the like, is described. To control the movement of the range selector valve and insure proper function thereof when shifting from one transmission range to another, thus avoiding transmission failures, the system prevents faulty manual shifting.
U.S. Pat. No. 3,919,510, which issued to Barnes on Nov. 11, 1975, discloses an electrically controlled shift mechanism for marine propulsion units. An electric shift control for a sterndrive for a boat includes a pair of snap action switches conjointly controlling an electro-responsive hydraulic shift to place the gears in a neutral position, a forward drive position or a reverse drive position or condition. Each of the switches is a single pole, double throw unit having a movable spring-loaded contact pole with a pair of alternate positions engaging first and second fixed contacts. A first switch has the movable contact connected to a power supply and provides power to a first drive position contact or in the alternate to provide power to a power transfer contact connected to the movable contact of the second switch.
U.S. Pat. No. 3,919,964, which issued to Hagen on Nov. 18, 1975, describes a marine propulsion reversing transmission with hydraulic assist. The device comprises a reversing transmission located in a propulsion unit and connecting a drive shaft to a propeller shaft and shiftable between neutral, forward drive, and reverse drive condition, together with a mechanical linkage extending in the propulsion unit and connected to the reversing transmission for operating the reversing transmission in response to movement of the mechanical linkage, and a hydraulic arrangement actuated in response to initial movement of the mechanical linkage for assisting and moving the mechanical linkage to operate the reversing transmission.
U.S. Pat. No. 4,958,138, which issued to Hawranek et al. on Sep. 18, 1990, describes a resistive position indicator. The indicator has an elongated resistive element with an electrical terminal at each end and a tap which can be brought into contact with the resistive element. A contact point divides the resistive element into two portions and is movable along the resistive element, so that the resistance ratio between the two portions of the resistive element can be varied within wide limits.
U.S. Pat. No. 5,340,341, which issued to Yoshimura on Aug. 23, 1994, describes a power assisting mechanism for a marine propulsion unit. It comprises a single source of hydraulic power, a steered device, a gear shift member, steering and gear shift control mechanism connected to their respective members and first and second power assist devices connected to the gear shift and steering control mechanism for power assist. A single substantially constant output hydraulic pump supplies an essential contact level of fluid power for the first and second power assist devices to assist the operator in controlling the steering and gear shift controls.
U.S. Pat. No. 5,488,860, which issued to Speck et al. on Feb. 6, 1996, describes an apparatus for determining the position of a piston in a fluidic actuator. Apparatus for determining the position of a piston in a hydraulically or pneumatically operated actuator including a fixed position, rotatable shaft having a pair of attached pins, each pin offset from the center of the shaft is described. The pins are positioned on either side of a drive ring located about the circumference of the piston. When the piston moves in either direction, one of the pair of pins will remain in contact with the drive ring and cause unidirectional rotation of the shaft. In order to detect piston position, a sensor is mounted to detect shaft rotation.
U.S. Pat. No. 6,015,364, which issued to Kolb et al. on Jan. 18, 2000, describes electronic gear shift assist circuitry. The circuit for reducing the clutch wear of a transmission on a marine propulsion system during the shift process by anticipating the probable shifting forces and providing an ignition kill signal before the shift forces can build to an unacceptable level is described.
U.S. Pat. No. 6,659,911, which issued to Suzuki et al. on Dec. 9, 2003, describes a shift assist system for an outboard motor. The system regulates the torque of the engine to ensure proper effortless shifting. The system recognizes open circuit or short circuit faults and nevertheless enables the torque of the engine to be reduced to facilitate easy gear selection.
U.S. Pat. No. 6,755,703, which issued to Erickson on Jun. 29, 2004, discloses a hydraulically assisted gear shift mechanism for a marine propulsion device. The mechanism provides a hydraulic cylinder and piston combination connected by a linkage to a gear shift mechanism. Hydraulic pressure can be provided by a pump used in association with either a power trim system or a power steering system. Hydraulic valves are used to pressurize selected regions of the hydraulic cylinder in order to actuate a piston which is connected, by an actuator, to the gear shift mechanism.
U.S. Pat. No. 6,840,888, which issued to Winquist et al. on Jan. 11, 2005, describes hydraulic-electronic control systems for marine vessels. The systems and methods for controlling shift and throttle of an electronically controlled power train are described. The system includes a throttle or shift controller having an operating range. A hydraulic slave is in fluid communication with the controller such that a movement of the controller within its operating range causes a flow or displacement of fluid between the controller and the hydraulic slave. The hydraulic slave has a shaft that rotates in response to the fluid flow between the controller and the hydraulic slave.
U.S. Pat. No. 6,845,683, which issued to Tarui et al. on Jan. 25, 2005, describes a shifting transfer mechanism. The mechanism includes a limit switch that sends an open-close signal of the switch contacts out to a control mechanism according to a shifting sequence. The shift contacts detect the position of a slider which is moved by a thrust actuator, during shifting in the range of 4H engagement to the range of N engagement. Therefore, if one of the switch contacts is faulty, the other switch detects shifting between 4H and N.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
In marine propulsion systems that utilize a shift assist mechanism, such as a hydraulically actuated piston, it would be significantly beneficial if a simple and compact position sensing system could be incorporated to determine the position of the shift assisting mechanism within the range of forward, neutral, and reverse positions.